When Wyatt and Gary come back from their first evening out with Lisa, they encounter Chet atop the stairs. When Chet first appears, his cigar is quite short. Later when we see Chet atop the stairs, the cigar appears much longer.
Although the movie takes place in the fictional town of Shermer, Illinois, the police car that chases Gary and Deb is clearly an LAPD interceptor. However, the rear facing yellow lights should flash on a LAPD car. The ones shown burn solid.
The fake drivers license Lisa gives Wyatt to get into the bar would be rejected by any bar bouncer in Illinois. Besides being cut crooked, the drivers license number doesn't match the name, sex, and birth date information shown on the license. Bouncers know that Illinois drivers license numbers can be decoded to yield that data. The number shown on the license should belong to a female born in 1951 whose last name begins with P.
When the cherry ICEE is poured over Wyatt's and Gary's heads, there is way more ICEE than could be held in that cup. Indeed, after the cup is thrown down afterward it appears to still have quite a bit in it.